Petroleum heater



Aug. 9, 1955 L. A. MEKLER PETROLEUM HEATER 5 Sheets-Sheet l /6 INVENTOR.ev Men/er Flled Oct 3 1950 FlE l HTTOR/VE YS Allg- 9, 1955 l.. A. MEKLER2,714,878

PETROLEUM HEATER Filed 001;. 3, 1950 '5 Sheets-Sheet 2 INVENTOR. ev A./V/@//ef- ATTORA/E V5 Aug. 9, 1955 L. A. MEKLER PETROLEUM HEATER 5Sheets-Sheet 3 Filed 001;. 5, 1950 l l l I n INVENTUR. eV ,47. Me/er BYq QM;

Allg- 9, 1955 1 A. MEKLER 2,714,878

PETROLEUM HEATER Filed Oct. 3, 1950 5 Sheets-Sheet 4 FlE E INVENTOR. evf4. Me/ev Aug 9, 1955 l.. A. MEKLER 2,714,878

PETROLEUM HEATER Filed Oct. 5, 1950 5 Sheets-Sheet 5 FIE 7 INVENTOR. evA Me/er QZ/w @.M;

United States Patent O PETROLEUM HEATER Lev A. Mekler, Palo Alto, Calif.Application October 3, 1950, Serial No. 188,187 3 Claims. (Cl. 122-235)This invention relates to an apparatus and method for heating fluids andparticularly to an apparatus and method for effectively utilizing theheat produced in such a device.

In the past it has been common practice to heat fluids by passing themthrough tubular conduits which may be placed in banks adjacent therefractory surfaces forming the enclosure of the apparatus. With thetubes so positioned, that portion of each tube which is exposed directlyto the source of heat absorbs approximately twice as much heat as thesurface of the tube which is adjacent to or facing the refractorysurface.

It is an object of this invention to provide a device of this characterwhich increases the portion of radiant heat supplied by re-radiation andreflection to the surface of the tube adjacent to or facing therefractory surface. This will permit higher average rates of heat inputalong the whole circumference of the tube surface for any given maximumrates on the portion of the surface exposed directly to the source ofheat.

As I have previously pointed out, various heaters have utilizedre-radiating walls adjacent banks of tubes. However, said radiatingwalls are normally planes or cylinders of a diameter many times thediameter of the tubes so that a secton of the radiating wall immediatelybehind or corresponding to a pair of tubes is substantially planar,whereby radiant rays passing between the tubes normal to the reradiatingwall or striking the same at right angles are reflected and re-radiatedback into the furnace, thereby missing the tubes. Only those raysstriking the re-radiating wall at an angle are reilected and re-radiatedto the tubes. Because of the cosine rule of radiant heat intensity, theslanted rays are weaker than the normal rays so that with the continuousplanes or cylindrical surfaces not only is a portion of the rays fallingupon these surfaces not utilized to supply heat to portions of the tubesfacing these surfaces, but the re-radiation from the remainder of therays is of relatively lower intensity than from the normal rays.

In addition to reflecting the heat rays and the reected rays, which canbe considered as single linear rays following the cosine rule of heatintensity, these surfaces also reradiate the heat. Re-radiation producesa spherical sector of radiant rays in which the individual rays alsofollow the rule of cosine. A at surface or a curved surfacesubstantially parallel with the periphery of the tube bank and behindthe tubes, therefore, re-radiates to the tubes only a part of theradiant rays within the sector.

. The rays so utilized are not as strong as those reflected between thetubes back to the source of heat. It is an object of my invention todeect to the back surfaces of the tubes the major portion of the radiantheat not absorbed directly by the surfaces facing the source of heat. Afurther object of this invention is to provide a heater which is soconstructed that combustion gases generated Within the heater will beprevented from channeling.

Fresh combustion gases ilowing through a heater towards an outletlocated at or near the top or the bot- 'ice tom of the heater have atendency to channel themselves through only a portion of the crosssection of the heater and thus to produce relatively hotter and colderzones Within the heater. One defect of prior heaters has been unevendistribution of heat due to the tendency of an appreciably large portionof the total combustion gases to channel themselves to the outlet withthe result that one portion of the heater would be heated at higherrates of heat input than another portion. Attempts to overcome thischanneling by placing bailes in the stream of heated gases or byrestricting the flow of gases by a damper in the stack and by usingother means of restricting the flow of heat by a common outlet from theheater to the atmosphere have been unsuccessful unless such obstructionso reduced the cross section near the outlet as to impose a positivepressure on the heater chamber. This is undesirable because it preventsoperation of the heater under natural draft and thus requires operationwith forced draft and use of mechanical power to supply air required forcombustion. Also even a small positive pressure in the heater requires agas-tight setting which is often not practical and is always moreexpensive than a setting for a heater operating under negative pressureor draft, no matter how small the negative pressure or draft may be.

It is a further object of this invention to provide a tubular heater inwhich there is a uniformity of heat input to the various portions of thebank of tubes and a uniformity of heat along the length ofthe tubeswithout the use of positive gas pressure in the heater chamber.

It is also an object of this invention to obtain more uniform heatdistribution around the circumference of each tube than can be obtainednormally in similar heater structures.

In some operations, if the variations of heat distribution aresufficiently great and the material being treated is suflicientlysensitive to heat treatment, a portion of the material being heated willbe overtrea'ted or a portion of the same will be undertreated, whichwill adversely affect quality and yield of the product desired. Moreuniform heat distribution obtained in a heater assures more uniform heattreatment to the whole body of the material being processed and,therefore, results in optimum yield and quality of the product.

Other objects and advantages of this invention will appear from thefollowing specication taken in conjunc tion with the accompanyingdrawings in. which:

Figure 1 illustrates, in cross section, a circular heater incorporatingmy invention;

Figure 2 is a cross-sectional View of a heater taken along the lines 2 2of Figure l;

Figure 3 is an enlarged detail showing the arrangement and positioningof `the tubes and baffles;

Figure 4 is an enlarged fragmentaryl View taken along the line 4 4 ofFigure 3;

Figure 5 is an enlarged detail of a tube and baie arrangementillustrating, by arrows, the .heat rays directed toward the tube by thebaffle;

Figure 6 illustrates the embodiment of my invention in a heater of thetype employing horizontal or substantially horizontal tubes;

Figure 7 is a cross-sectional view taken along the line 7 7 of Figure 6;and

Figure 8 is an enlarged cross-sectional detail illusttatL ing theposition of the tubes, baffles, and the means for supporting the same.

My heater consists of a shell 10 adapted to be supported by members 11.Shell 10 may be made of any conventional material and of any sizedesired and, as shown in Figure l, may be circular in cross-section. Atthe lower end of the shell 10, I have provided a truncated conicalportion 12 which is adapted to accommodate one 3 or more burners 13 ofany conventional type adapted to receive and burn suitable fuel materialand to discharge the products of combustion into the interior of theshell 10. At the upper end of the shell 1) I provide a similar truncatedportion which serves as a` gathering duct 14 for the products ofcombustion and directs them to the exhaust or outlet stack 16.

The uid conducting conduits 17 consist of a plurality of vertical tubesor conduits adapted to carry the fluid to be treated and which aredisposed in a single circular row coaxial with the shell 10. The tubes17 may be arranged in series to provide in effect one stream throughoutthe heater or may be so connected as to form two or more such parallelstreams. The manner of connecting the conduits 17 is substantiallyconventional and may vary to suit particular conditions.

As illustrated in Figure 1, I provide a horizontal partition 18 near theupper end of the heater. The horizontal partition 18 is constructed ofany suitable material and is mounted in such a manner that itsubstantially blocks thepow of gases from the burner 13 to the stack 16and divides the heater into a lower primary zone and an upper secondaryzone.

I also provide a plurality of vertical bales 21 arranged generally asillustrated in Figures l and 2. Those bales 21 below the partition 18are arranged in a circle outside of the bank of tubes 17 while thosebales 21 above the partition 18 are arranged in a circle within the bankof tubes 17.

As illustrated particularly in Figure 3, the baffles 21 provide a pairof curvilinear surfaces 22. The surfaces 22 are preferably made of ahigh temperature oxidation resistant alloy which will retain, at theoperating conditions at which the heater is adapted to be operated, itsrelatively low emissivity and relatively high reflecting power. Inaddition to smooth high temperature alloy sheets, glazed or semiglazedrefractories may be used. In the event alloy sheets are used the baflies21 may be constructed as illustrated in Figure 3, in which the sheetforming the surfaces 22 may be formed generally as illustrated andsecured to a at plate 23 which may be formed of less expensive material.The void between the plate 23 and the front of the balile may be filledwith loose granular insulation 24 of any particular type.

The baille surfaces 22 facing the tubes 17 form portions of cylinderswhose radius is from one and one-half to two and one-half times thediameter of one of the tubes 17. The bafes 21 and tubes 17 serve to formconstantly decreasing passages 25 for the gases from the center of theheater to the area beyond the batles and are so positioned as to form aVenturi-like section for the discharge of gases into the annular space26 around the bales. The space 26 between baflles 21 and the interior ofthe shell 10 forms an annular ue for the passage of gases upwardly intothe area above the partition 18. As is more particularly illustrated inFigure l, the bafes 21 in that portion of the shell above the partition18 are placed within the circular bank of tubes 17 in such a manner thatthey form decreasing Venturi-like passageways to openings between theballles 21 permitting the ow of gases from within the annular flue 26 tothe gathering duct 14 immediately underlying the stack 16.

I also provide a number of horizontal separator plates 27 which act aspartitions within the baies and as spacers to support the granularmaterial within the batiies and as guides for the bafes 21 with respectto the tubes 17. The girth members 28 secure the bales 21 as indicated.In addition, the girth members 28 provide a suitable support and aunitary structure for thepbaffles and may be mounted in any suitablemanner upon the shell 10 to provide additional rigidity to the'entirestructure.

Operation lof the device may briefly be described as follows: Let it beassumed that heat is generated within the burner 13 as indicated, withthe result that combustion gases are Vdistributed in the 'area withinthe bank of' Cir tubes 17. The combustion gases would normally flowdirectly from the burner 13 to the stack 16. However, the area of thecross section of the heater is normally considerably greater than thearea required to carry the fresh gases from the burners 13 to the stack16 and unless means are provided to disperse the fresh gases through themain body of the gas in the heater, the gases leaving the burner 13 willform a channel through the main body of the gas in the heater. Partition18 prevents passage of gas directly to the stack 16 so that the gasescan leave the heater only through the passageways between the tubes 1'7and baffles 21. Because the gases can leave the heater only along theperiphery of the gas body by passing over and between the tubes, thefresh gases must pass through and mix with the main body of the gasesbefore leaving the heater. This results in substantial uniformity oftemperature of gas nearthe tubes along horizontal planes. In addition,the tubes serve to form a cold plane in the path of the gases. This coldperipheral plane on the outside of the mass of gas and the hot centerwithin the mass induce appreciable thermal siphon circulation upward inthe center and downward along the tubes 17, which further assists inestablishing uniform heat distribution in the heater and permits the useof high input rates without fear that Zones of local overheating maygreatly exceed these rates.

As has previously been pointed out, the front portions 22 of the baflles21 are so shaped and so placed with respect to each other as to form aVenturi-like section for discharge of gases into the annular space 26between the shell 10 and the outer walls 23 of the baies 21. TheVenturi-like shape of the passageways 25 from the heater into theannular space 26 serves to reduce the pressure drop and to provide thehighest velocity near the relatively narrow space near the gas outlet.The deposit of soot or ash on the tubes or the baffles is minimizedbecause there are no sharp turns in the path of the gases or long narrowpassageways along the tubes, as is the case with tubes with extendedsurfaces in a relatively long narrow passage as exist in some heaters,and as is the case with very long narrow passages lined withrefractories as utilized in other types. The bales will, therefore,retain their effectiveness over a long period of time.

Furthermore, in addition to dening the path of cornbustion gases fromthe center of the heater to the annular Space 26 surrounding the tubes17 and baies 21 and directing relatively high velocity gases against theshielded portion of the circumference of each of the tubes, the baiiiesserve as re-radiating and reliecting surfaces i to supply heat to theshielded half of the tubes to a considerably greater extent than wouldbe supplied by the cylindrical surface of the shell 1t) of the heaterwhere there are no bafes. In Figure 5 I have attempted to representschematically by arrows the heat rays directed toward the surface 22 ofthe baffles 21. The arrows directed toward the tubes represent thecentral radii of the spherical sectors of re-radiation and the paths ofreflected heat. It Will be seen that practicaiiy all of the 1re-radiatedand reflected heat is directed toward the back half or shielded Surfacesof the tubes with very little of the heat re-radiating or beingreflected back into the center of the heater, Because the walls of thebaies are preferably made of a material having relatively low emissivityand relatively high reflecting power7 a greater portion of the incidentradiant heat striking the surface of the baffles will be reflected heatwhich will follow more closely the paths shown by the arrows.

Calculations indicate that with the shape and space relationship of thebafes as shown and assuming that the baffles are made of an alloy withan emissivity of 0.45, the combined equivalent emissivity of the batliesfor reradiation and reection is close to 6.95 as against 0.63 for aplaneyor a large diameter cylindrical refractory surface. The equivalentemissivity of the .batlles will be Somewhat lower if the 'baffles aremade of a material of higher emssivity and lower reflecting power thanherein specified. The baffles, therefore, are instrumental in increasingthe amount of radiant heat available to the shielded half of the tubesby approximately 50%.

It will be apparent, therefore, that the use of these baliles results inhigher rates of radiant heat input to the shielded half of the tubesurface for a given maximum heat ux on the exposed half and thus permitsthe use of higher average heat input rates along the total circumferenceof the tube for a given maximum rate on the exposed surface, or to putit in another way, results in lower maximum rates for the same averagecircumferential rates than can be obtained with bare tubes without suchbailles, or with tubes placed in front of a at or planar re-radiatingsurface.

It would appear that the increased radiant heat absorption by theshielded half of the tubes due to the batlles will result in an increaseof approximately 15% in the average heat input rates about the totalcircumference of the tubes. Superimposed convection from the gases addsL from 1,000 to 1,500 B. t. u. per square foot to the heat supplied tothe tubes so that the total increase in average heat transfer rates fora given maximum heat flux on the exposed face is 18 to 20%. By way ofexample, without bailles and at an average rate of heat input of 10,000B. t. u. per square foot, the exposed half of the tubes will have anaverage rate of 14,700 B. t. u. and a maximum ilux of 17,500, whereasthe shielded half will absorb merely 5,300 B. t. u. With my baffles andat the same average and maximum rates on the exposed half, the shieldedhalf will absorb an average of 9,000 B. t. u. and the average for thetotal circumference will be approxiately 11,800 B. t. u. The advantagesof the bales are even more pronounced at the higher average heat inputrates. Without baffles and assuming average rates of 12,000 B. t. u. themaximum flux is approximately 21,000. With baffles, average rates of14,200 B. t. u. are obtained with the same flux. The maximum flux willbe over 25,000 if 14,200 B. t. u. average rates are obtained without thebales.

The problem of channeling gases is an old one and is well recognized.For example, others have sought to accomplish the same result, that is,to obstruct the ow of gases from the heater and to break up the totalowv into a number of small streams by placing baffles in the normal pathof the gases. However with one type of heater with which I am familiar,l have found that the gases in their natural ow, due to the hydraulicsof hot gases to ow upwards, will not flow through all of the baffles atsubstantialy uniform rate and will tend to channel.

In a heater incorporating my invention, however, gas hydraulics does noteffect the ow of gases through the bafdes. On the contrary, the bafesmake gases flow in a direction substantially at right angles to thehydraulic effect and from the periphery of the main body or stream ofgases. By the utilization of the partition 18, therefore, the hydrauliceffect of the flow of gases is overcome and substantially eliminated. Byproviding equally spaced slots of equal section between the baffles, thegases will tend to flow through the slots uniformly in the same plane.

Other designers have utilized baille bricks and have placed the tubeswithin longitudinal annular spaces to effect convection components byincreasing the velocity of gases around the otherwise shieldedcircumference of the tubes. Devices of this type have shielded the backsof the tubes from radiation. `On the contrary it will be observed thatmy design not only does not obstruct radiant heat from passing betweenthe tubes but redirects this heat to the back surface of the tubes,thereby increasing the radiant heat input by reflecting forward to theback of the tube a major portion of the heat that would otherwise bere-radiated into the furnace and lost to the back of the tube. In theprior devices of which I speak all rays which are normal or at rightangles to the sur` face are reflected back into the furnace through thesame aperture between the tubes through which they entered. These raysmiss the tubes. Only the slanted rays, which are the weakest, arereflected to the rear side of the tube. By virtue of the curvilinearsurfaces which I provide, substantially all rays falling upon thesurfaces are reected towards the back or shielded portion of the tubesurface at an angle equal to the angle formed by the ray and the radiusof curvature of the surface at the point thereby increasing the radiantheat input to the otherwise protected portion of the tube. This isstrictly true only for reflected heat rays which I have considered assingle linear rays for the purposes of this discussion. However, it willbe noted that the smooth alloy or glazed ceramic which I utilize willprovide the maximum of reection and will, therefore, act as described toa greater extent than dull relatively rough surfaces with lowerreflecting properties. However, the surfaces I provide are alsoeffective even though to a somewhat lesser extent to reradiation.Re-radiation I prefer to consider as being spherical with a sector ofradiant rays radiating from the point hit by a ray from the interior ofthe furnace. By the law of cosines applied to radiation the rays nearthe center of the re-radiation sector will be the strongest while thosenear the edge of the sector will be the weakest. In the event thebaffles behind the tubes were flat, the strongest rays, that is thosenearest the center of the sector, would tend to be re-radiated back intothe center of the heater and those rays nearest the outer edge of thesector would strike the tube. With the bailles, the rays near the centerof the sector are deiiected towards the tube surface facing them.

In addition to acting as directional reflecting and reradiating surfacesfor radiations from the heat source to increase radiant heat input tothe tube surfaces they face,

the baffles act as solid partitions between tubes which preventre-radiation between the tube surfaces. Without such partitions thesurface of one tube faces the relatively cold heat absorbing surfaces ofthe adjoining tubes so that the effectiveness of the tubes is reducedappreciably. The baffles isolate the tube surfaces they face fromadjoining tube surfaces and substitute relatively high temperature andsubstantially nonabsorbing surfaces which materially increase theeffectiveness of the tube surfaces facing the baffles by shading thetube surfaces from each other.

Prior devices have also sought to increase the uid heat componentsupplied from the combustion gases to the rear of the tubes by providingspaced refractories in close proximity to that portion of the tubeshielded from the source of heat and by causing the combustion gases,which have given up a major portion of their heat by radiation to theexposed portions of the tube bank and to the refractories, to pass aboutand in intimate contact with shielded portions of the tube at relativelyhigh velocity through the spaces provided between the refractory shapesand the tubes. Such devices, however, are effective for heat transferonly by convection and reduce rather than increase radiant heat input tothe surfaces affected so that they are less effective in their over-alleffect than the present design.

In the embodiment of my invention illustrated in Figures 6, 7 and 8, Iillustrate a petroleum heater in which the tubes or conduits arehorizontal or substantially horizontal.

As illustrated particularly in Figures 6 and 7, the heater consists of ashell 31 which is adapted to be supported by members 32. The shell 31may be made of any conventional material and of any size desired, and,as particularly illustrated in Figure 7, is preferably square orrectangular in section. At the lower end of the shell 31 I have provideda truncated pyramidal portion 33 which is adapted to accommodate one ormore burners 34 of any particular typeV adapted to receive and burnsuitable fuel material and to discharge the products of combustion intothe interior of the shell 31. At the top yof the shell 31 I provide asimilar truncated pyramidal portion 36 which servesas a gathering ductfor the products of combustion and directs them to the exhaust or outletstack 37.

. The uid conducting conduits 38, which are adapted to carry the fluidto be treated, are disposed in a vertical plane parallel With the wallsof the heater. The conduits 38 may be arranged in series to provide ineffect one stream throughout the heater or they may be so connected asto form two or more parallel streams. The manner of connecting theconduits 38 is substantially conventional and may vary to suitparticular conditions.

As illustrated in Figure 6, I provide a horizontal partition 39 near thetop of the heater. The partition 39 is constructed of any suitablematerial and may be mounted in such a manner that it substantiallyblocks the flow of gases from the burners 34 to the stack 37 and dividesthe heater into a lower primary zone and an upper secondary zone.

I also provide a plurality of horizontal bafes 41 which aresubstantially identical to the bales 21 previously described herein.Those bafes 41 below the partition 39 are arranged in a vertical planeoutside of the bank of tubes 38 While those baffles 41 above thepartition 39 are raised in a vertical plane within the bank of tubes 41.

As illustrated particularly in Figure 8 the baffles 41, like the baffles21 previously described herein, provide curvilinear surfaces 42 which,together with the tubes 38, serve to form constantly decreasing passages43 for the gases from the center of the heater to the area beyond thebaies and are so positioned as to form a Venturi-like section for thedischarge of gases into the space 44 around the bafes.

The tubes 38 are supported at their ends by the vertical tube sheets 46and intermediate supports 47. The intermediate supports 4'7 are attachedto the structural members of the side walls 31 of the heater, with theexception, however, that the intermediate supports above the partition39 may be suspended from the structural members of the heater.

The operation of the heater constructed as indicated in Figures 6, 7 and8 will be substantially identical with the heater illustrated in Figuresl to 4 inclusive and will provide the same pattern of gas ow and heatdistribution. The functioning of the baies 41 is the same as haspreviously been described herein in connection with Figures l to 4inclusive.

It must be borne in mind that my heater can be equipped with aconvection section, air preheater or waste heater boiler if it iseconomically justifiable to further cool the gases before they areexhausted from the heater.

It will be obvious from the foregoing that I have provided a heaterconstruction consisting of an arrangement of tubes and bailles wherebythe maximum re-radiation and reection of heat to the rear shieldedportion of the tubes is obtained, and whereby the rear shielded portionof the tube is subjected to superposed convection by gases passing overthis portion at relatively high velocity before the gases leave theheating chamber.

In addition, I have provided a device in which the channeling ofcombustion gases with its attendant disadvantages is substantiallyeliminated.

I have provided a device providing for more uniform heat distributionabout the periphery of the heater along the length of the tube andaround the circumference of the tube than can be obtained without thisdevice. Greater'uniformity at the same horizontal plane is obtained bythe means provided to draw off the gases from the heater through thespaces between the baffles and at an angle with the direction of flowinduced by the stack effect of the height of the heater. In addition,because of the increased thermal circulation within the heater chamberbrought about by the thermal Siphon effect of the relatively coldperiphery formed by the tubes and the relatively hot center of the gasbody, the gas temperatures at the top and bottom of the heater tend toequalize' so that the heatV input along the length of each particulartube is also equalized. -Also, because of the increased re-radiation andreflection, together with the convection component produced by theVenturi-like section between the walls of the baiiies and the tubes, thedifference in heat input to the shielded and exposed portions of thetube is decreased so that the heat input around the circumference of thetube tends to be much more uniform.

I claim:

l, In a uid heater, a housing, a horizontally disposed partition withinsaid housing dividing the interior of said housing into an upper chamberand a lower chamber burner means for conducting combustion within saidlower chamber, a plurality of fluid heating tubes grouped to form a wallarea in said lower chamber about said burner means, a plurality of iluidheating tubes grouped to form a wall area in said upper chamber, aplurality of spaced bafes in said lower chamber interposed between thetubes and spaced from the tubes in said lower chamber, said bales insaid lower chamber facing the burner means in a position between thefluid heating tubes in said lower chamber and the housing to provide aspace between the bales and the housing leading to the upper chamber, aplurality of spaced bales in said upper charnber interposed between andspaced from the fluid heating tubes in the upper chamber, said bafflesbeing oppositely faced to those in the lower chamber, each of thebaffles in the upper and lower chambers having two heat reflectingsurfaces for reflecting heat towards the adjacent tubes whereby eachtube receives heat reections from two such surfaces formed on adjacentbales, said heat reilecting surfaces in section having radiiconsiderably greater than the radii of said tubes to increase theportion of radiant heat supplied by reradiation and reection to thetubesv opposite the source of heat, said baflies being spaced from eachother and said tubes to provide in section Venturi-like flow passagestherebetween whereby the velocity of ow of the combustion gases throughthe Venturi-like passages increases and is the greatest at the side ofthe tubes opposite the source of heat to thereby minimize the deposit ofsoot and ash on the tubes and baffles, said combustion gases passing outof the lower chamber past the heating tubes in the lower chamber throughthe battles in the lower chamber into the space between the baies andthe housing to pass upwardly into the upper chamber past the heatingtubes in said upper chamber and past the bales in said upper chamber.

2. In a uid heater, a housing, a horizontally disposed partition withinsaid housing dividing the interior of said housing into an upper chamberand a lower chamber, burner means for conducting combustion within saidlower chamber, a plurality of fluid heating tubes grouped to form a wallarea in said lower chamber about said burner means, a vplurality offluid heating tubes grouped to form a wall area in said upper chamber,said tubes in said upper and lower chambers being interconnected and insection embracing equal areas, a plurality of spaced baffles in saidlower chamber interposed between the tubes and `spaced Vfrom the tubesin said lower chamber, said baffles in the lower chamber facing theburner means and being positioned between the uid heating tubes on saidlower chamber and the l housing to provide a space between the battlesand the housing, a plurality of spaced baffles in said upper chamberinterposed between and spaced from the fluid heating tubes in the upperchamber, said bafes being oppositely faced to those in the lowerchamber, each baffle in the upper and lower chambers having two heatreilecting surfaces for reecting heat towards adjacent tubes wherebyeach tube receives heat reflection from two such surfaces formed onadjacent bafes, said heat refleeting surfaces in section having radiiconsiderably greater than the radii of said tubes to increase theportion of radiant heat supplied by reradiation and reflection to thetubes opposite the source of heat, said bailles being spaced from eachother and said tubes to provide in section Venturi-like ow passagestherebetween whereby the velocity of ow of combustion gases through theVenturi-like passages increases and is the greatest at the side of thetubes opposite the source of heat to thereby minimize the deposit ofsoot and ash on the tubes and bafiles, and means for connecting thebaffles to the tubes in such a manner that the batlies will follow themovement of the tubes.

3. In a fluid heater, burner means for conducting combustion, aplurality of fluid heating tubes grouped to form a wall area about theburner means, and a plurality of spaced heat reecting baiiies interposedbetween the tubes on the sides of said tubes opposite the source ofheat, each baille having two reflecting surfaces for reflecting heattowards two adjacent tubes whereby each tube receives heat reflectionfrom two of said surfaces formed 0n adjacent baffles, said heatreflecting surfaces in section having radii considerably greater thanthe radii of said tubes to increase the portion of radiant heat suppliedby re-radiation and reflection to the sides of the tubes opposite thesource of heat, said baffles being spaced from each other and said tubesto provide in section venturi-like low passages therebetween whereby thevelocity of ow of the combustion gases through the venturi-like passagesincreases and is the greatest at the side of the tubes opposite thesource of heat to thereby minimize the deposit of soot and ash on thetubes and baies, said baies comprising smooth, high temperature alloysheets formed to provide said heat reilecting surfaces, a flat platesecured to the rear of said heat reiiecting surfaces, separator platesspaced along the length of the heat reecting surfaces, the space betweensaid heat reflecting surfaces and said at plate being iilled withgranular insulation, said separator plates serving to support thegranular insulation and also to position the baffles with respect to theheating tubes.

References Cited in the file of this patent UNITED STATES PATENTS1,881,275 Huff Oct. 4, 1932 2,147,610 Zimmerman Feb. 14, 1939 2,338,295Mekler Jan. 4, 1944 2,479,544 Schauble Aug. 16, 1949 2,641,234 Mekler etal. June 9, 1953 FOREIGN PATENTS 22,775 Great Britain Nov. 28, 1893242,198 Great Britain Nov. 5, 1925

